1. Field of the Invention
The present invention relates to a semiconductor optical device and a method of forming the semiconductor optical device.
2. Prior Arts
S. Farwell et al., “InP Coherent Receiver Chip with High Performance and Manufacturability for CFP2 Modules”, Optical Fiber Communication Conference 2014, USA, OSA Technical Digest, W1I.6, March 2014.
An optical device applicable to a coherent optical system provides a multi-mode interferometer (MMI) having, what is called, an optical hybrid, with a plurality of photodiodes (PDs) that convert optical signals provided from the optical hybrid into electrical signals. The PDs couple with the MMI through optical waveguides. In particular, when an MMI is integrated on a substrate with the PDs in the optical semiconductor device for the coherent optical system, conductive semiconductor layers are commonly formed in the MMI, the optical waveguides, and the PDs. The respective PDs are electrically isolated by forming trenches therebetween. That is, forming the PDs within respective mesas physically isolated from neighbor mesas by the trenches, the PDs may be electrical isolated. However, because the trenches are not extended within the optical waveguides, only existing between the PDs; electrically conduction paths are left through the conductive semiconductor layers in the optical waveguides.